Golf club head

Abstract

This golf club head achieves improvement in initial ball speed, high initial speed area, launch angle, spin, feel of impact, and durability.　When the tensile strengths of a first layer 36, a second layer 38, and a third layer 40 constituting a face part 14 are denoted by S1, S2, and S3, S3≥S1>S2 is satisfied. By striking a ball with a face surface 1402, the first layer 36, the second layer 38, and the third layer 40 constituting the face part 14 are deformed. In this case, since the second layer 38, which has the lowest tensile strength and is the softest, is sandwiched between the first layer 36 and the second layer 38, which have high tensile strength and are hard, the face part 14 is deformed within the range of elastic deformation, which makes it easier for the first layer 36 to deform as a spread surface rather than a point. Thus, it is advantageous in increasing the contact area between the face surface 1402 and the ball, and in securing more contact time between the face surface 1402 and the ball.

Description

Golf club head

[0001] The present invention relates to a golf club head.

[0002] A golf club head has been proposed in which the face is composed of a first metal plate and a second metal plate that supports the first metal plate via multiple ribs (see Patent Document 1). In this golf club head, the first metal plate is displaced in a direction along the face surface upon impact, thereby reducing the amount of spin on the ball.

[0003] Patent No. 4340177

[0004] However, with the above-mentioned conventional technology, there is a risk that the multiple ribs will deform excessively when hitting the ball, and the face portion will not return to its original shape even when the ball leaves the face portion, in other words, there is a risk that the face portion will deform excessively, and there is room for improvement in terms of improving the ball initial velocity, high initial velocity area, launch angle, spin, hit feel, and durability. The present invention has been made in consideration of the above circumstances, and its object is to provide a golf club head that is advantageous in terms of improving the ball initial velocity, high initial velocity area, launch angle, spin, hit feel, and durability.

[0005] To achieve the above object, one embodiment of the present invention is a golf club head having a hollow structure in which at least a portion of a face portion is composed of a first layer constituting a face surface, a second layer located on the opposite side of the first layer from the face surface, and a third layer located on the opposite side of the second layer from the first layer, wherein when the tensile strengths of the first layer, second layer, and third layer are S1, S2, and S3, respectively, S3 ≥ S1 > S2. Also, one embodiment of the present invention is characterized in that the hardness of the first layer is equal to or greater than durometer hardness D75 and equal to or less than Vickers hardness HV520, the hardness of the second layer is equal to or greater than durometer hardness A10 and equal to or less than durometer hardness D60, and the hardness of the third layer is equal to or greater than durometer hardness HV520. In one embodiment of the present invention, the first layer has a tensile modulus of elasticity of 8 GPa to 240 GPa, the second layer has a tensile modulus of elasticity of 0.5 MPa to 3000 MPa, and the third layer has a tensile modulus of elasticity of 10 GPa to 240 GPa. In one embodiment of the present invention, the first layer has a thickness of 0.1 mm to 1.5 mm, the second layer has a thickness of 0.1 mm to 1.0 mm, and the third layer has a thickness of 2.0 mm to 5.0 mm. In one embodiment of the present invention, the first layer is made of any one of a metal material, a synthetic resin material, and a fiber-reinforced resin material, the second layer is made of any one of a double-sided tape, a synthetic resin material, and an elastic material, and the third layer is made of any one of a metal material, a synthetic resin material, and a fiber-reinforced resin material. In one embodiment of the present invention, the third layer has a thin portion that is thinner than other portions, the thin portion being formed by a recess formed in the first layer in an open manner on a front surface of the third layer facing the first layer, and the second layer is disposed by filling the recess. In another embodiment of the present invention, the front surface of the third layer excluding the recess is superimposed on the first layer.In one embodiment of the present invention, the golf club head comprises a hollow head body including a face outer periphery in which an opening is provided except for the outer periphery of the face body, and a crown portion, a sole portion, and a side portion connected to the face outer periphery, wherein a plate-shaped third face member constituting the third layer is provided inside the face outer periphery on the interior side of the head body, a plate-shaped second face member constituting the second layer is attached to the third face member inside the face outer periphery by overlapping it, and a plate-shaped first face member constituting the first layer is attached to the second face member inside the face outer periphery by overlapping it, and the outer periphery of the third face member is butted against the inner periphery of a frame-shaped inner periphery plate portion of the face outer periphery and attached by welding, and a bead generated during the welding is accommodated in a bead accommodating space provided across the outer periphery of the third face member and the inner periphery of the attachment plate portion on the side away from the interior of the head body, and the bead accommodating space is covered by the second face member and the first face member.In one embodiment of the present invention, the golf club head comprises a hollow head body having openings formed by removing the face portion, a portion of the crown portion near the face portion, a portion of the sole portion near the face portion, and a portion of the side portion near the face portion, and the third face member constituting the third layer comprises a third face body corresponding to the face portion, and a third flange protruding from the outer periphery of the third face body toward the head body, and the second face member constituting the second layer comprises a second face body attached to the third face body by being superimposed thereon, and a second face member protruding from the outer periphery of the second face body toward the head body by being superimposed thereon and attached to the third flange, the portion of the crown portion near the opening, the portion of the sole portion near the opening, and the portion of the side portion near the face portion. and two flanges, and the first face member constituting the first layer comprises a first face member superimposed on and attached to the second face member, and a first flange protruding from the outer periphery of the first face member toward the head body and superimposed on the second flange, and the tip end face of the third flange is butted against the tip end face of the crown member, the tip end face of the sole member and the tip end face of the side member which form the opening, and is attached by welding, and a bead produced during the welding is accommodated in a bead accommodating space provided across the outer periphery of the third flange, the outer periphery of the crown member, the outer periphery of the sole member and the outer periphery of the side member on the side away from the inside of the head body, and the bead accommodating space is covered by the second face member and the first face member.

[0006] According to one embodiment of the present invention, the first, second, and third layers constituting the face portion deform when the ball is struck with the face surface. Since the soft second layer is sandwiched between the hard first and second layers, the face portion deforms within an elastic deformation range. Therefore, the first layer is more likely to deform as a broad surface rather than a point, thereby increasing the contact area and contact time between the face surface and the ball. Therefore, by ensuring a large contact area and contact time, the recoil effect reduces the amount of backspin on the ball, resulting in a high launch angle and low spin on the ball, thereby increasing the ball's flight distance. Recoil is the phenomenon in which an elastic twist generated inside the ball due to contact between the ball and the face surface attempts to return to its original position. In other words, it is an internal spin in the forward direction, opposite to backspin. Therefore, the greater the recoil, the lower the amount of backspin on the ball. Furthermore, because the face portion bends over a wide area, the initial velocity of the ball increases over a wide area of ​​the face surface, which is advantageous for expanding the high initial velocity area. The soft second layer also reduces stress on the third layer when hitting the ball, which is advantageous in ensuring the durability of the face over a wide area of ​​the face. The soft second layer also limits the volume, pitch, and reverberation of the impact sound to a comfortable range for golfers, resulting in a moderately soft feel on impact, which is advantageous in improving the feel on impact over a wide area of ​​the face.

[0007] 1 is a front view of a golf club head according to a first embodiment, as seen from the front of the face surface. (A) is a cross-sectional view taken along line A-A in FIG. 1, and (B) is a partial cross-sectional view showing a modified example. (A)-(F) are cross-sectional views schematically showing the configuration of the face portion. (A) is a cross-sectional view schematically showing the face portion of a second embodiment, and (B) is a cross-sectional view schematically showing the face portion of a third embodiment. (A) is a cross-sectional view of a golf club head according to a fourth embodiment, and (B) is a partial cross-sectional view showing a modified example. (A) is a cross-sectional view of a golf club head according to a fifth embodiment. (A)-(E) are cross-sectional views showing a manufacturing process of a golf club head according to a sixth embodiment. (A) is a cross-sectional view showing a first modified example of the golf club head according to the first embodiment, where (A) shows the state before assembly and (B) shows the state after assembly. (B) is a cross-sectional view showing a second modified example of the golf club head according to the first embodiment, where (A) shows the state before assembly and (B) shows the state after assembly. 10A and 10B are cross-sectional views showing a first modified example of a golf club head according to a fourth embodiment, where (A) shows the state before assembly and (B) shows the state after assembly. 10B are cross-sectional views showing a second modified example of a golf club head according to a fourth embodiment, where (A) shows the state before assembly and (B) shows the state after assembly. 10C are diagrams showing evaluation results of an experimental example under condition 1 in the embodiment. 10D are diagrams showing evaluation results of an experimental example under condition 2 in the embodiment. 10E are diagrams showing evaluation results of an experimental example under condition 3 in the embodiment. 10F are diagrams showing evaluation results of an experimental example under condition 4 in the embodiment.

[0008] First Embodiment First, a first embodiment will be described. As shown in FIGS. 1 and 2A, in this embodiment, a golf club head 10A is a hollow wood-type golf club head (driver). A head body 12A of the golf club head 10A, excluding a face portion 14 (described later), is made of a metal material or a fiber-reinforced plastic material (FRP), or a combination of a metal material and a fiber-reinforced plastic material. Examples of the metal material include one or more of stainless steel, maraging steel, pure titanium, a titanium alloy, and an aluminum alloy. Examples of such titanium alloys include 6-4Ti and 8-1-1Ti. Examples of the fiber-reinforced plastic material include a carbon fiber-reinforced plastic material (CFRP). The golf club head 10A includes a face portion 14, a crown portion 16, a sole portion 18, and a side portion 20. The golf club head 10A has a hollow structure in which the interior surrounded by the face portion 14, crown portion 16, sole portion 18, and side portion 20 is a hollow portion 22 (see FIG. 2A). The face portion 14 has a vertical height and extends horizontally.

[0009] The crown portion 16 has a thickness smaller than that of the face portion 14 and extends rearward from the upper portion of the face portion 14. The surface exposed to the outside of the face portion 14 is a face surface 1402 that strikes the ball. A hosel 28 that connects to a shaft S is provided on the crown portion 16 at a position on the face surface 1402 side and closer to the heel 24, and the golf club 100 is configured by connecting the shaft S to the hosel 28. The sole portion 18 extends rearward from the lower portion of the face portion 14. The side portion 20 extends between the crown portion 16 and the sole portion 18, passing through the back of the face, between the toe 24 side edge and the heel 26 side edge of the face portion 14.

[0010] 2A, the golf club head 10A includes a hollow head main body 12A, a plate-shaped first face member 30, and a plate-shaped second face member 32. The face portion 14 of the golf club head 10A is composed of the first and second face members 30, 32 and a face portion plate 34 of the head main body 12A. In other words, the face portion 14 of the golf club head 10A is composed of a first layer 36 constituting a face surface 1402, a second layer 38 located on the opposite side of the first layer 36 from the face surface 1402, and a third layer 40 located on the opposite side of the second layer 38 from the first layer 36. The first layer 36 is composed of the first face member 30. The second layer 38 is composed of the second face member 32 and is attached to the surface of the first face member 30 opposite the face surface 1402. The third layer 40 is formed by the face plate 34 of the head main body 12A, and the second face member 32 is attached to and superimposed on the outer surface of this face plate 34. In this embodiment, the head main body 12A and the face plate 34 are formed of the same material, such as 8-1-1Ti (cast material). When the tensile strengths of the first layer 36, second layer 38, and third layer 40 are defined as material strengths S1, S2, and S3, respectively, the relationship S3≧S1>S2 is satisfied.

[0011] (Hardness) The hardness of the first layer 36 was a durometer hardness of D75 or greater and a Vickers hardness of HV520 or less. The hardness of the second layer 38 was a durometer hardness of A10 or greater and a durometer hardness of D60 or less. The hardness of the third layer 40 was a durometer hardness of D85 or greater and a Vickers hardness of HV520 or less. Having the hardnesses of the first layer 36, second layer 38, and third layer 40 within the above ranges is advantageous for improving the ball's initial velocity, high initial velocity area, launch angle, spin, feel, and durability, as described below. If the hardnesses of the first layer 36, second layer 38, and third layer 40 were less than the above ranges, the face portion 14 would deform excessively (no longer within the elastic deformation range, as described below) when hitting the ball, resulting in energy loss when hitting the ball and reducing the effectiveness of improving the ball's initial velocity, high initial velocity area, launch angle, spin, feel, and durability. If the hardness of the first layer 36, the second layer 38, and the third layer 40 exceeds the respective ranges, the deformation (amount of deflection) of the face portion 14 when hitting the ball will be insufficient, and the effects of improving the ball's initial velocity, high initial velocity area, launch angle, spin, hitting feel, and durability will be reduced.

[0012] (Tensile Modulus) The tensile modulus of the first layer 36 is 8 GPa or more and 240 GPa or less. The tensile modulus of the second layer 38 is 0.5 MPa or more and 3000 MPa or less. The tensile modulus of the third layer 40 is 10 GPa or more and 240 GPa or less. Having the tensile modulus of the first layer 36, second layer 38, and third layer 40 each within the above range is advantageous for improving the ball initial velocity, high initial velocity area, launch angle, spin, feel on impact, and durability, as described below. If the tensile modulus of the first layer 36, second layer 38, and third layer 40 each is less than the above range, the face portion 14 will deform excessively upon impact (no longer within the elastic deformation range, as described below), resulting in energy loss upon impact and reducing the effectiveness of improving the ball initial velocity, high initial velocity area, launch angle, spin, feel on impact, and durability. If the tensile modulus of elasticity of the first layer 36, the second layer 38, and the third layer 40 exceeds the above range, respectively, the deformation (amount of deflection) of the face portion 14 when hitting the ball will be insufficient, and the effects of improving the ball's initial velocity, high initial velocity area, launch angle, spin, feel on impact, and durability will be reduced.

[0013] (Thickness) The thickness of the first layer 36 is 0.1 mm or more and 1.5 mm or less. The thickness of the second layer 38 is 0.1 mm or more and 1.0 mm or less. The thickness of the third layer 40 is 2.0 mm or more and 5.0 mm or less. Having the thicknesses of the first layer 36, second layer 38, and third layer 40 within the above ranges is advantageous for improving the ball initial velocity, high initial velocity area, launch angle, spin, feel, and durability, as described below. If the thicknesses of the first layer 36, second layer 38, and third layer 40 are less than the above ranges, the face portion 14 will deform excessively upon impact (it will no longer be within the elastic deformation range, as described below), resulting in energy loss upon impact and reducing the effectiveness of improving the ball initial velocity, high initial velocity area, launch angle, spin, feel, and durability. If the thickness of the first layer 36, the second layer 38, and the third layer 40 exceed the respective ranges, the deformation (amount of deflection) of the face portion 14 when hitting the ball will be insufficient, and the effects of improving the ball's initial velocity, high initial velocity area, launch angle, spin, hitting feel, and durability will be reduced.

[0014] (Materials) The first layer 36 is made of a metal material, a synthetic resin material, or a fiber-reinforced resin material. The second layer 38 is made of a double-sided tape, a synthetic resin material, or an elastic material. The third layer 40 is made of a metal material, a synthetic resin material, or a fiber-reinforced resin material. Elastic materials used for the second layer 38 include rubber and resin. Examples of rubber include natural rubber, polybutadiene rubber, styrene-butadiene rubber, and isoprene rubber. Examples of resin include ionomer resin, urethane resin, polyester resin, and polyamide resin. Elastic materials include the elastic adhesive 42 (FIG. 3A) described below and hot-melt adhesives (sheet adhesives: thermoplastic sheet adhesives). The hardness ranges from 40 to 90 Shore A. Softer adhesives are often used. Examples of metal materials used for the third layer 40 include a rolled plate of 6-4Ti, a titanium alloy.

[0015] The head volume is, for example, 150 cc or more and 460 cc or less, and is applicable to golf club heads 10A such as drivers, fairway woods, and utilities.

[0016] Next, specific configuration examples of the face portion 14 will be described with reference to Figures 3(A) to 3(F). Note that the dimensions, hardness, and material names in the following configuration examples are merely examples and do not limit the present invention. The configuration of the third layer 40 is common to all of the examples shown in Figures 3(A) to 3(F). In the face portion 14 shown in Figure 3(A), the first layer 36 is made of CFRP (carbon fiber reinforced plastic) with a thickness of 0.75 mm. The second layer 38 is made of an elastic adhesive 42 with a thickness of 0.2 ± 0.1 mm (durometer hardness A 87), and the second layer 38 is bonded to the first layer 36 and the third layer 40 by the adhesive force of this elastic adhesive 42. The third layer 40 is made of a titanium alloy with a thickness of 2.0 mm to 5.0 mm.

[0017] In the face portion 14 shown in FIG. 3B, the first layer 36 is composed of a 0.75 mm thick CFRP. The second layer 38 is composed of a 0.1 mm thick urethane sheet (durometer hardness A 90 degrees). The third layer 40 is composed of a 2.0 mm to 5.0 mm thick titanium alloy. The second layer 38 is bonded to the CFRP of the first layer 36 with a 0.25 mm thick epoxy adhesive 44A and to the titanium alloy of the third layer 40 with a 0.25 mm thick epoxy adhesive 44B. The hardness of the epoxy adhesives 44A and 44B is, for example, approximately 75 to 90 degrees durometer D. Note that the hardness of the epoxy adhesives 44A and 44B used in the second embodiment and the third embodiment described below all meets the above hardness specifications. Therefore, the first layer 36 is composed of the epoxy adhesive 44A, and the third layer 40 is composed of the epoxy adhesive 44B.

[0018] In the face portion 14 shown in FIG. 3C, the first layer 36 is composed of 0.75 mm thick CFRP. The second layer 38 is composed of 0.25 mm thick double-sided tape (foaming agent) 46. Various types of double-sided tape (foaming agent) can be used, including those with acrylic foam, urethane foam, polypropylene, and polyester substrates. The double-sided tape 46 of the second layer 38 is adhered to the first layer 36 with a 0.25 mm thick epoxy adhesive 44A and to the third layer 40 with a 0.25 mm thick epoxy adhesive 44B. The third layer 40 is composed of a titanium alloy with a thickness of 2.0 mm to 5.0 mm. Therefore, the first layer 36 is composed of the epoxy adhesive 44A, and the third layer 40 is composed of the epoxy adhesive 44B. In this example, epoxy adhesives 44A and 44B are used to reinforce the adhesive strength of double-sided tape 46, but the epoxy adhesives 44A and 44B may be omitted if there is no need to reinforce the adhesive strength of double-sided tape 46. Also, second layer 38 may be formed using only the acrylic foam base material, urethane foam base material, polypropylene base material, or polyester base material, excluding the adhesive component used in double-sided tape 46.

[0019] In the face portion 14 shown in Figure 3(D), the first layer 36 is made of 0.2 mm thick SUS (stainless steel sheet). The second layer 38 is made of 0.2 ± 0.1 mm thick elastic adhesive 42 (durometer hardness A 87), and the second layer 38 is bonded to the first layer 36 and the third layer 40 by the adhesive force of this elastic adhesive 42. The third layer 40 is made of a titanium alloy having a thickness of 2.0 mm to 5.0 mm.

[0020] In the face portion 14 shown in FIG. 3(E), the first layer 36 is composed of a 0.2 mm thick stainless steel (SUS) sheet. Alternatively, a 0.4 mm thick titanium sheet or a 0.6 mm thick aluminum sheet can be used. The second layer 38 is composed of a 0.1 mm thick urethane sheet (durometer hardness A 90). The third layer 40 is composed of a titanium alloy with a thickness of 2.0 mm to 5.0 mm. The second layer 38 is bonded to the SUS (stainless steel) first layer 36 with a 0.25 mm thick epoxy adhesive 44A and to the titanium alloy third layer 40 with a 0.25 mm thick epoxy adhesive 44B. Therefore, the first layer 36 is composed of the epoxy adhesive 44A, and the third layer 40 is composed of the epoxy adhesive 44B.

[0021] In the face portion 14 shown in FIG. 3(F), the first layer 36 is composed of a 0.2 mm thick SUS (stainless steel sheet). The second layer 38 is composed of a 0.25 mm thick double-sided tape (foaming agent) 46. The double-sided tape 46 of the second layer 38 is adhered to the first layer 36 with a 0.25 mm thick epoxy adhesive 44A and to the third layer 40 with a 0.25 mm thick epoxy adhesive 44B. The third layer 40 is composed of a titanium alloy with a thickness of 2.0 mm to 5.0 mm. Therefore, the first layer 36 is composed of the epoxy adhesive 44A, and the third layer 40 is composed of the epoxy adhesive 44B. Alternatively, the second layer 38 may be composed of only an acrylic foam substrate, a urethane foam substrate, a polypropylene substrate, or a polyester substrate, excluding the adhesive component used in the double-sided tape 46. In this example, epoxy adhesives 44A and 44B are used to reinforce the adhesive strength of the double-sided tape 46, but if there is no need to reinforce the adhesive strength of the double-sided tape 46, the epoxy adhesives 44A and 44B can be omitted.

[0022] Next, a manufacturing method of the golf club head 10A according to the present embodiment will be described. As shown in FIGS. 2A and 3A to 3F, first, the golf club head 10A is manufactured, excluding the first layer 36 and the second layer 38 of the face portion 14. Next, the second layer 38 is attached to the third layer 40 of the face portion 14 by overlapping it, and then the first layer 36 is attached to the second layer 38 by overlapping it. The second layer 38 and the first layer 36 can be attached using the elastic adhesive 42, double-sided tape 46, or epoxy adhesives 44A and 44B, as described above. For example, if a thermosetting adhesive is used as the epoxy adhesives 44A and 44B, the second layer 38 and the first layer 36 are overlapped on the third layer 40 and then hot-pressed to harden the epoxy adhesives 44A and 44B. Alternatively, if the outermost layer is made of CFRP, the CFRP may be first hardened (at 150°C for 60 minutes) and then the hardened CFRP may be bonded with an adhesive. The cured CFRP may be heated at 120° C. for 60 minutes to conform to the shape of the bottom layer.

[0023] 2A , the outer surface (face surface 1402) of the first layer 36 is higher than the outer surface of the third layer 40 by the thickness of the first layer 36 and the second layer 38, and an annular step is formed between the outer surface of the third layer 40 and the outer peripheral surfaces of the first layer 36 and the second layer 38. To eliminate this step, an annular plate-shaped synthetic resin 48 having the same thickness as the step is bonded between the outer peripheral surfaces of the first layer 36 and the second layer 38 and the outer surface of the third layer 40, and then the outer peripheral portion of the first layer 36 and the synthetic resin 48 are polished to form a smooth curved surface connecting the outer surface of the third layer 40 and the outer surface (face surface 1402) of the first layer 36. Then, a ring-shaped coating (not shown) is applied over the outer peripheral portion of the outer surface (face surface 1402) of the first layer 36, the curved surface of the synthetic resin 48, and the outer surface of the third layer 40. By applying this type of painting, the step is concealed and the appearance of the golf club head 10A is improved. In this manner, the golf club head 10A is manufactured, having a face portion 14 including the first layer 36, the second layer 38, and the third layer 40. Note that instead of providing this type of synthetic resin 48, as shown in FIG. 2(B), in order to eliminate the annular step portion of the first layer 36 and the second layer 38 formed on the outer surface of the third layer 40, the first layer 36 and the second layer 38 may be machined into tapered surfaces and a paint 49 may be applied to the surfaces of the tapered surfaces to conceal the step and improve the appearance of the golf club head 10A.

[0024] Next, the effects will be described. In the golf club head 10A of this embodiment, when the tensile strengths of the first layer 36, second layer 38, and third layer 40 constituting the face portion 14 are defined as material strengths S1, S2, and S3, respectively, the relationship S3 ≥ S1 > S2 is satisfied. Therefore, when a ball is struck with the face surface 1402, the first layer 36, second layer 38, and third layer 40 constituting the face portion 14 deform. However, since the second layer 38, which has the lowest tensile strength and is soft, is sandwiched between the first and second layers 36 and 38, which have high tensile strength and are hard, the face portion 14 deforms within an elastic range. Therefore, the first layer 36 is more likely to deform as a surface with an extension rather than as a point, which is advantageous for increasing the contact area between the face surface 1402 and the ball and ensuring a long contact time between the face surface 1402 and the ball.

[0025] Here, deformation within the elastic deformation range of the second layer 38 does not mean deformation within the range in which the face portion 14 does not undergo plastic deformation, but rather refers to deformation in which the shape of the face portion 14 nearly returns to its pre-deformation shape when a ball struck with the face surface 1402 separates from the face surface 1402. In other words, when a ball struck with the face surface 1402 separates from the face surface 1402, the shape of the face portion 14 is still significantly deformed and significantly deviates from its pre-deformation shape, and the face portion 14 does not return to its pre-deformation shape. If the face portion 14 undergoes deformation that is not within the elastic deformation range, there is a disadvantage in that there is a large energy loss and a decrease in initial velocity.

[0026] When the contact area and contact time between the ball and the face surface 1402 are increased, the recoil effect reduces the amount of backspin on the impacted ball, resulting in a high launch angle and low spin, thereby increasing the ball's flight distance. Furthermore, since the face portion 14 deforms within its elastic deformation range, the face portion 14 bends over a wide area, resulting in a high initial velocity of the ball over a wide area of ​​the face surface 1402, which is advantageous for expanding the high initial velocity area. Furthermore, the soft second layer 38 reduces stress during impact, thereby reducing stress generated in the third layer 40, which is advantageous for ensuring the durability of the face portion 14 over a wide area of ​​the face surface 1402. Furthermore, the soft second layer 38 limits the volume, pitch, and reverberation of the impact sound to a comfortable range for the golfer, resulting in a moderately soft impact feel, which is advantageous for improving the impact feel over a wide area of ​​the face surface 1402.

[0027] Here, we will explain the tensile strength, hardness, tensile modulus, and thickness of the first layer 36, second layer 38, and third layer 40. In the present invention, it is important that the soft layer (second layer 38) undergoes appropriate surface deformation during elastic deformation while maintaining the durability of the golf club head. As a result, the high initial velocity area can be expanded without reducing initial velocity, enabling increased distance with a high launch angle and moderately low backspin, and achieving a soft feel on impact. High tensile strength is necessary to ensure durability. The outermost layer (first layer 36) and the innermost layer (third layer 40) experience greater deformation (tensile and compressive stress) upon impact than the intermediate layer (second layer 38), so high-strength materials must be used. On the other hand, the soft layer (second layer 38) that undergoes surface deformation during elastic deformation must be appropriately soft. For example, if it is too soft, energy loss will occur, resulting in a reduced initial velocity. Hardness is an important factor in ensuring the soft layer (second layer 38) undergoes appropriate surface deformation during elastic deformation. In addition, bending rigidity (Bending rigidity (EI) = Longitudinal Young's modulus (E) x Moment of inertia (I)), where Longitudinal Young's modulus (E) is the tensile modulus of elasticity in this specification. Bending rigidity is also important, and the tensile modulus of elasticity and thickness of each material are interrelated. In other words, the four factors of tensile strength, hardness, tensile modulus of elasticity, and thickness are intricately intertwined, and properly arranging these factors is an important point for the golf club head according to the present invention.

[0028] Next, first and second modified examples of the first embodiment will be described with reference to FIGS. 8 and 9 . In the first and second modified examples, the thickness of the second layer 38 is maintained at a constant dimension. As shown in FIGS. 8B and 9B , a coating 49 is applied to eliminate the annular step between the first layer 36 and the second layer 38 formed on the outer surface of the third layer 40, as in FIG. 2B . As shown in FIGS. 8A and 8B , in the first modified example, the first layer 36 (first face member 30) constituting the face surface 1402 is made of 0.75 mm thick CFRP, the second layer 38 (second face member 32) is made of an elastic adhesive 42 (or a hot-melt adhesive), and the third layer 40 (face plate portion 34) is made of a 6-4 Ti rolled plate. On the front surface of the third layer 40 (rolled 6-4Ti plate), i.e., on the front surface where the face plate 34 faces the second layer 38, a plurality of cylindrical protrusions 3402, each 0.25 mm high and 2 mm in diameter, are provided at 15 mm intervals in the toe-heel and crisscross directions and protrude toward the second layer 38. The tips of the plurality of protrusions 3402 abut against the rear surface of the first layer 36 (CFRP), thereby ensuring a gap of 0.25 mm between the front surface of the third layer 40 (rolled 6-4Ti plate) and the rear surface of the first layer 36 (CFRP), and elastic adhesive 42 is filled in this gap to form the second layer 38 having a thickness of 0.25 mm.

[0029] In the second modified example shown in Figure 9, the first layer 36, the second layer 38, and the third layer 40 have the same configurations as those in the first modified example. As shown in Figures 9A and 9B, in the second modified example, a plurality of cylindrical protrusions 3002, each 0.25 mm high and 1 mm in diameter, protruding toward the second layer 38 are provided at 15 mm intervals in the toe-heel and crisscross directions on the rear surface of the 0.75 mm-thick first layer 36 (CFRP), i.e., the rear surface where the first face member 30 faces the second layer 38. The tips of the plurality of protrusions 3002 abut against the front surface of the third layer 40 (6-4Ti rolled plate), thereby ensuring a 0.25 mm gap between the front surface of the third layer 40 (6-4Ti rolled plate) and the rear surface of the first layer 36 (CFRP). An elastic adhesive 42 is filled in this gap to form the second layer 38 having a thickness of 0.25 mm. In both the first and second modified examples, the shape of the protrusions 3402, 3002 is not limited to a cylindrical shape, as long as a gap can be secured between the front surface of the third layer 40 (rolled 6-4Ti plate) and the rear surface of the first layer 36 (CFRP). According to the first and second modified examples, the simple structure of providing a plurality of protrusions 3402, 3002 is advantageous in ensuring a constant thickness for the elastic adhesive 42 that constitutes the second layer 38.

[0030] Second Embodiment Next, a second embodiment will be described with reference to FIG. 4A. In the following embodiments, parts and components similar to those of the first embodiment are denoted by the same reference numerals, and their description will be omitted. The following description will focus on the differences. As shown in FIG. 4A, a thin-walled portion 4002 is formed in the third layer 40, which is thinner than the other portions. The thin-walled portion 4002 is formed as an open recess 4004 in the first layer 36 on the front surface of the third layer 40 facing the first layer 36. The first layer 36 is formed of a 0.2 mm thick stainless steel (SUS) sheet or a 0.75 mm thick CFRP (CFRP) sheet. The second layer 38 is disposed by filling the recess 4004. The third layer 40 is formed of a titanium alloy having a thickness of 2.0 mm to 5.0 mm. Specifically, the second layer 38 is formed by stacking a 0.3 mm-thick (durometer hardness A 90 degrees) urethane sheet 50A formed with a shape and thickness corresponding to the recess 4004 and filling the recess 4004, and a 0.1 mm-thick (durometer hardness A 90 degrees) urethane sheet 50B provided on the front surface of the third layer 40, including the recess 4004. The second layer 38 is bonded to the SUS (stainless steel sheet) or CFRP of the first layer 36 with a 0.25 mm-thick epoxy adhesive 44A, and to the titanium alloy of the third layer 40 with a 0.13 mm-thick epoxy adhesive 44B. Thus, the first layer 36 and the third layer 40 are formed including the epoxy adhesives 44A and 44B.

[0031] According to the second embodiment, not only can the same effects as those of the first embodiment be achieved, but by providing a recess 4004 on the front surface of the third layer 40, a thin-walled portion 4002 can be formed by partially thinning the thickness of the third layer 40, thereby forming a thickness-varying structure in the face portion 14. Therefore, for example, forming an annular thin-walled portion 4002 surrounding the center of the face surface 1402 increases the amount of deflection of the face portion 14, which is advantageous for increasing the initial velocity of the ball and increasing the flight distance. While a thickness-varying structure can be formed in the face portion 14 by providing a recess 4004 on the rear surface of the third layer 40, providing a thickness-varying structure in the face portion 14 by providing a recess 4004 on the front surface of the third layer 40 as in the embodiment can increase surface deformation closer to the striking surface than by providing a recess on the rear surface of the third layer 40, which is advantageous for expanding the high initial velocity area, ensuring a recoil effect, and improving durability. The shape and number of the thin-walled portion 4002 that constitute the thickness-varying structure are not limited.

[0032] (Third Embodiment) Next, a third embodiment will be described with reference to FIG. 4B . The third embodiment is a modification of the second embodiment, and differs from the second embodiment in that the front surface of the third layer 40, excluding the recess 4004, is directly superimposed on the first layer 36 without the second layer 38 interposed therebetween. Specifically, the first layer 36 is composed of a 0.2 mm thick SUS (stainless steel sheet) or a 0.75 mm thick CFRP (prepreg sheet). The second layer 38 is composed of a 0.2 mm thick (durometer hardness A 90) urethane sheet 50C shaped to correspond to the recess 4004, filling the recess 4004. The third layer 40 is composed of a titanium alloy having a thickness of 2.0 mm to 5.0 mm. Specifically, the front surface of the second layer 38 and the front surface of the third layer 40 excluding the recessed portion 4004 are bonded to the SUS (stainless steel sheet) or CFRP of the first layer 36 with a 0.25 mm thick epoxy adhesive 44A, and the portion of the second layer 38 filling the recessed portion 4004 is bonded to the recessed portion 4004 (titanium alloy) of the third layer 40 with a 0.13 mm thick epoxy adhesive 44B. That is, the first layer 36 is configured to contain the epoxy adhesive 44A, and the third layer 40 is configured to contain the epoxy adhesive 44B. Therefore, the front surface of the third layer 40 excluding the recessed portion 4004 and the first layer 36 are directly superimposed. This third embodiment also achieves substantially the same effects as the second embodiment.

[0033] (Fourth Embodiment) Next, a fourth embodiment will be described with reference to FIG. 5A . In the fourth embodiment, the mutual attachment structure of the first layer 36, the second layer 38, and the third layer 40, i.e., the mutual attachment structure of the first face member 52, the second face member 54, and the third face member 56 described below, is the same as that of the first embodiment, and therefore description thereof will be omitted. A golf club head 10B of the fourth embodiment includes a hollow head main body 12B, a plate-shaped first face member 52, a plate-shaped second face member 54, and a plate-shaped third face member 56. The head main body 12B includes a face outer periphery 60 having an opening 58 in the face portion 14 except for the outer periphery of the face portion 14, and a crown portion 16, a sole portion 18, and a side portion 20 connected to the face outer periphery 60. Like the head main body 12B of the first embodiment, the head main body 12B is made of a metal material or a fiber-reinforced plastic (FRP) material, or a combination of a metal material and a fiber-reinforced plastic material. When a titanium alloy is used as the metal material for the head main body 12B, an example of the titanium alloy is 8-1-1Ti. The outer peripheral face portion 60 includes a frame-shaped outer peripheral plate portion 62 that forms the outer periphery of the face surface 1402, a frame-shaped protruding plate portion 64 that protrudes from the inner periphery of the frame-shaped outer peripheral plate portion 62 into the head main body 12B, and a frame-shaped inner peripheral plate portion 66 that protrudes inward from the tip of the frame-shaped protruding plate portion 64. The face portion 14 of the golf club head 10B is made up of a first layer 36 that forms the face surface 1402, a second layer 38 located on the opposite side of the first layer 36 from the face surface 1402, and a third layer 40 located on the opposite side of the second layer 38 from the first layer 36.

[0034] The third layer 40 is composed of a third face member 56, which is disposed inside the face outer periphery 60 and inside the head main body 12B. Specifically, the outer periphery of the third face member 56 is butted against the leading end surface of the inner peripheral plate portion 66 of the face outer periphery 60 and welded. The third face member 56 is composed of a metal material manufactured by, for example, a rolled plate or forging. An example of such a metal material is a rolled plate of 6-4Ti, which is a titanium alloy. The third face member 56 is made of a 6-4Ti rolled plate, and its material is set so that its strength (tensile strength) is greater than that of the head main body 12B, which is made of 8-1-1Ti (cast material). This is to maintain durability so that the face portion 14 will not break when impacted with a ball. A bead accommodating space 68 is provided across the outer surface of the protruding plate portion 64 located away from the interior of the head body 12B and the outer surface of the outer periphery of the third face member 56, and a bead B created when the outer periphery end face of the third face member 56 is butted against the tip end face of the inner periphery plate portion 66 of the face outer periphery portion 60 and welded is accommodated in the bead accommodating space 68. The second layer 38 is composed of the second face member 54, and the second face member 54 is attached to the surface of the third face member 56 inside the outer periphery plate portion 62 of the face outer periphery portion 60 by overlapping it. The first layer 36 is composed of the first face member 52, and the first face member 52 is attached to the surface of the second face member 54 inside the outer periphery plate portion 62 of the face outer periphery portion 60 by overlapping it. The face surface 1402 is composed of the surface of the outer periphery plate portion 62 of the face outer periphery portion 60 and the surface of the first face member 52. The bead receiving space 68 is covered by the second face member 54 and the first face member 52. Note that it is optional to fill the bead receiving space 68 with resin, adhesive, or the like before covering the bead receiving space 68 with the second face member 54. Alternatively, a convex portion having a shape corresponding to the bead receiving space 68 may be formed in advance on the second face member 54, and the bead receiving space 68 may be filled with the convex portion.Furthermore, the appearance of the golf club head 10B may be improved by filling an annular gap 70 formed between the outer peripheral end surfaces of the first face member 52 and the second face member 54 and the outer peripheral plate portion 62 with resin or by covering the gap 70 with paint. Furthermore, as shown in Fig. 5B, when the outer peripheral end surfaces of the first face member 52 and the second face member 54 abut against the outer peripheral plate portion 62 without any gap and a boundary line is formed between them, the boundary line may be covered with paint 71 or the like to conceal the boundary line and improve the appearance of the golf club head 10B.

[0035] According to the fourth embodiment, not only can the same effects as those of the first embodiment be achieved, but also, because the bead receiving space 68, which receives the weld bead B formed by welding the third face member 56 to the head main body 12B, is covered by the second face member 54 and the first face member 52, the grinding of the weld bead B, which was previously required, can be omitted, which is advantageous in reducing the manufacturing cost of the golf club head 10B. It is also possible to weld the third face member 56 to the head main body 12B without forming a recess recessed toward the hollow portion 22 at the welded portion. However, if the weld bead B protrudes outward, grinding (machining) of the weld bead B would be necessary, which would increase manufacturing costs. Therefore, in the fourth embodiment, the bead receiving space 68 completely receives the weld bead B, eliminating the need to grind the weld bead B. Furthermore, the fourth embodiment can be optionally combined with the uneven thickness structures of the second and third embodiments.

[0036] Furthermore, in the fourth embodiment, the third face member 56 and the head body 12B can be made of different metal materials, with the third face member 56 being made of a metal material with higher strength than the head body 12B. For example, the third face member 56 can be made of a 6-4Ti rolled plate, and the head body 12B can be made of 8-1-1Ti. Furthermore, in the fourth embodiment, the third face member 56 and the head body 12B can be made of different materials, with the third face member 56 being made of a material with higher strength than the head body 12B. For example, the third face member 56 can be made of a 6-4Ti rolled plate, and the head body 12B can be made of CFRP.

[0037] In the fourth embodiment, the bead accommodating space 68 may not be provided, and the weld bead B formed by welding the third face member 56 and the head body 12B may be polished as in the conventional case, and the welded portion between the third face member 56 and the head body 12B may be covered with the second face member 54 and the first face member 52. However, the fourth embodiment is advantageous in terms of reducing manufacturing costs.

[0038] Next, first and second modified examples of the fourth embodiment will be described with reference to FIGS. 10 and 11 . In the first and second modified examples, the thickness of the second layer 38 is maintained at a constant dimension. For simplicity, the weld bead B formed by welding the plate-shaped third face member 56 to the opening 58 of the head body 12B, the bead receiving space 68, and other components are omitted from FIGS. 10 and 11 . Also, as shown in FIGS. 10B and 11B , a coating 71 is applied to cover the boundary between the outer peripheral end surfaces of the first face member 52 and the second face member 54 and the outer peripheral plate portion 62, as in FIG. 5B . 10(A) and 10(B), in the first modified example, the first layer 36 (first face member 52) constituting the face surface 1402 is made of CFRP with a thickness of 0.75 mm, the second layer 38 (second face member 54) is made of an elastic adhesive 42 (or a hot melt adhesive), and the third layer 40 (third face member 56) is made of a 6-4Ti rolled plate. A plurality of cylindrical protrusions 5602, each 0.25 mm high and 2 mm in diameter, protruding toward the second layer 38 are provided at intervals of 15 mm in the toe-heel and crisscross-sole directions on the front surface of the third layer 40 (6-4Ti rolled plate), i.e., on the front surface of the third face member 56 facing the second layer 38. Then, as the tips of the multiple protrusions 5602 abut against the rear surface of the first layer 36 (CFRP), the protrusions 5602 create a gap of 0.25 mm between the front surface of the third layer 40 (6-4Ti rolled plate) and the rear surface of the first layer 36 (CFRP), and by filling this gap with elastic adhesive 42, a second layer 38 having a thickness of 0.25 mm is formed.

[0039] 11A and 11B, the configurations of the first layer 36, the second layer 38, and the third layer 40 are the same as those of the first modified example. As shown in Figures 11A and 11B, in the second modified example, a plurality of cylindrical protrusions 5202, each 0.25 mm high and 1 mm in diameter, protruding toward the second layer 38 are provided at intervals of 15 mm in the toe-heel direction and the cross-sole direction on the rear surface of the 0.75 mm thick first layer 36 (CFRP), i.e., the rear surface where the first face member 52 faces the second layer 38. The tips of the multiple protrusions 5202 abut against the front surface of the third layer 40 (rolled 6-4Ti plate), thereby creating a 0.25 mm gap between the front surface of the third layer 40 (rolled 6-4Ti plate) and the rear surface of the first layer 36 (CFRP). Filling this gap with elastic adhesive 42 forms a 0.25 mm-thick second layer 38. In both the first and second modifications, the shape of the protrusions 5602, 5202 is not limited to a cylindrical shape, as long as it can create a gap between the front surface of the third layer 40 (rolled 6-4Ti plate) and the rear surface of the first layer 36 (CFRP). According to the first and second modifications, the simple structure of providing multiple protrusions 5602, 5202 is advantageous in ensuring a consistent thickness of the elastic adhesive 42 that constitutes the second layer 38. Of course, a structure similar to the first and second modifications can also be employed in the fifth embodiment described below.

[0040] Fifth Embodiment Next, a fifth embodiment will be described with reference to FIG. 6 . In the fifth embodiment, the attachment structure between the first layer 36, the second layer 38, and the third layer 40, i.e., the attachment structure between the first face member 72, the second face member 74, and the third face member 76 (described later), is the same as in the first embodiment, and therefore will not be described again. The golf club head 10C includes a hollow head main body 12C, a plate-shaped first face member 72, a plate-shaped second face member 74, and a plate-shaped third face member 76. The head main body 12C includes a crown portion 16, a sole portion 18, and a side portion 20, and further includes openings 78 formed by removing the face portion 14, a portion of the crown portion 16 closer to the face portion 14, a portion of the sole portion 18 closer to the face portion 14, and a portion of the side portion 20 closer to the face portion 14. The head main body 12C is made of a metal material or a fiber-reinforced plastic (FRP) material, or a combination of a metal material and a fiber-reinforced plastic material. When a titanium alloy is used as the metal material constituting the head main body 12C, an example of the titanium alloy is 8-1-1Ti. The face portion 14 of the golf club head 10C is made of a first layer 36 constituting a face surface 1402, a second layer 38 located on the opposite side of the first layer 36 from the face surface 1402, and a third layer 40 located on the opposite side of the second layer 38 from the first layer 36.

[0041] The third layer 40 is composed of a third face member 76, which includes a third face body 7602 corresponding to the face portion 14 and a third flange 7604 protruding from the outer periphery of the third face body 7602 toward the head body 12C. The third face member 76 is composed of a metal material manufactured by, for example, a rolled plate or forging. An example of such a metal material is a rolled plate of 6-4Ti, a titanium alloy. The material is set so that the strength (tensile strength) of the third face member 76 is greater than that of the head body 12C. The leading end surface of the third flange 7604 is butted against the leading end surfaces of the crown portion 16, the sole portion 18, and the side portion 20, which form the opening 78, and is welded to them. A bead accommodating space 80 is provided on the side away from the interior of the head body 12C, spanning the outer periphery of the tip of the third flange 7604, the outer periphery of the crown portion 16, the outer periphery of the sole portion 18, and the outer periphery of the side portion 20, and the weld bead B produced during welding is accommodated in the bead accommodating space 80.

[0042] The second layer 38 is composed of a second face member 74, and the second face member 74 includes a second face member 7402 that is attached by overlapping with the third face member 7602, and a second flange 7404 that protrudes from the outer periphery of the second face member 7402 toward the head body 12C, covers the bead accommodating space 80, and is attached by overlapping with the third flange 7604 and the portion of the crown portion 16 near the opening 78, the portion of the sole portion 18 near the opening 78, and the portion of the side portion 20 near the face portion 14.

[0043] The first layer 36 is composed of a first face member 72, which includes a first face member 7202 that is attached by overlapping with a second face member 7402, and a first flange 7204 that protrudes from the outer periphery of the first face member 7202 toward the head body 12C and is attached by overlapping with a second flange 7404. Therefore, the bead receiving space 80 is covered by the second face member 74 and the first face member 72. The first flange 7204, the second flange 7404, and the third flange 7604 correspond to the portions of the crown portion 16 near the face portion 14, the sole portion 18 near the face portion 14, and the side portion 20 near the face portion 14 that were removed by the opening 78. Before covering the bead receiving space 80 with the second face member 74, the bead receiving space 80 may be optionally filled with a resin or the like. Alternatively, a convex portion having a shape corresponding to the bead receiving space 80 may be formed in advance on the second face member 74, and the bead receiving space 80 may be filled with the convex portion.

[0044] As shown in FIG. 6 , the first flange 7204 (first layer 36) and the second flange 7404 (second layer 38) are elevated relative to the outer surface of the head body 12C by the thickness of the first layer 36 and the second layer 38, and an annular step is formed relative to the outer surface of the head body 12C by the leading end faces of the first flange 7204 and the second flange 7404. To eliminate this step, synthetic resin 82 of the same thickness as the step is bonded between the leading end faces of the first flange 7204 and the second flange 7404, the outer surface of the third layer 40, and the outer surface of the head body 12C. The first flange 7204 and the synthetic resin 82 are then polished to form a smooth curved surface connecting the outer surface of the head body 12C and the outer surface of the first flange 7204. Then, the outer surface of the first flange 7204, the curved surface of the synthetic resin, and the outer surface of the head body 12C are painted. By applying such a coating, the steps are concealed and the appearance of the golf club head 10C is improved.

[0045] According to the fifth embodiment, not only can the same effects as those of the first embodiment be achieved, but also, because the bead receiving space 80 that receives the weld bead B formed by welding the third face member 76 to the head main body 12C is covered with the second face member 74 and the first face member 72, the grinding work of the weld bead B that was conventionally required can be omitted, which is advantageous in reducing the manufacturing cost of the golf club head 10C. Furthermore, the fifth embodiment can be optionally combined with the uneven thickness structures of the second and third embodiments.

[0046] Furthermore, in the case of the fifth embodiment, the third face member 76 and the head body 12B can be made of different metal materials, with the third face member 76 being made of a metal material with higher strength than the head body 12B. For example, the third face member 76 can be made of a 6-4Ti rolled plate, and the head body 12C can be made of 8-1-1Ti. Furthermore, in the case of the fifth embodiment, the third face member 76 and the head body 12B can be made of different materials, with the third face member 76 being made of a material with higher strength than the head body 12B. For example, the third face member 76 can be made of a 6-4Ti rolled plate, and the head body 12C can be made of CFRP.

[0047] Sixth Embodiment Next, a sixth embodiment will be described with reference to FIG. 7 . The golf club head 10D of the sixth embodiment is a modified example of the fifth embodiment, in which the bead receiving space 80 is not provided, and the weld bead B formed on the outside of the third face member 76 and the head main body 12D by welding the third face member 76 to the head main body 12D is polished as in the conventional case, and the welded portion between the third face member 76 and the head main body 12C is covered with the second face member 74 and the first face member 72. As in the fifth embodiment, the sixth embodiment also has the same attachment structure as the first embodiment, i.e., the same attachment structure as the first face member 72, the second face member 74, and the third face member 76, and therefore a description thereof will be omitted. 7A and 7B, by welding the third face member 76 and the head main body 12D together, weld beads B are formed on the inside (the hollow portion 22 side) of the third face member 76 and the head main body 12D and on the outside (the opposite side from the hollow portion 22) of the third face member 76 and the head main body 12D. Next, as shown in Fig. 7C, the weld beads B formed on the outside (the opposite side from the hollow portion 22) of the third face member 76 and the head main body 12D are polished so that the outside of the third face member 76 and the outside of the head main body 12D are connected by a smooth curved surface. 7(D), the second layer 38 (second face member 74) is superimposed on and attached to the third layer 40 (third face member 76), and then the first layer 36 (first face member 72) is superimposed on and attached to the second layer 38 (second face member 74). At this time, as in the fifth embodiment, an annular step is formed on the outer surface of the head main body 12D by the tip end faces of the first flange 7204 and the second flange 7404. To eliminate this step, synthetic resin 82 of the same thickness as the step is bonded between the tip end faces of the first flange 7204 and the second flange 7404, the outer surface of the third layer 40, and the outer surface of the head main body 12D. The first flange 7204 and the synthetic resin 82 are then polished to form a smooth curved surface connecting the outer surface of the head main body 12D and the outer surface of the first flange 7204.Then, a coating is applied to the outer surface of the first flange 7204, the curved surface of the synthetic resin, and the outer surface of the head main body 12D. This coating conceals the step and improves the appearance of the golf club head 10D. Alternatively, instead of applying the synthetic resin 82, as shown in FIG. 7E , in order to eliminate the annular step on the tip end surfaces of the first flange 7204 and the second flange 7404 formed on the outer surface of the head main body 12D, the tip portions of the first flange 7204 and the second flange 7404 may be tapered, and the tapered surfaces may be coated with a coating 83 to conceal the step and improve the appearance of the golf club head 10D. This method also achieves the same effects as the fifth embodiment.

[0048] Next, experimental examples of the present invention will be described. Figures 12 to 15 are diagrams showing experimental results of golf club heads according to the present invention. A sample golf club head was created for each experimental example, and the following five evaluation items were measured to determine indices (evaluation points), and the total score of the five indices was calculated.

[0049] (1) High Initial Velocity Area (Sweet Area) Forty-five impact points Pi were set at equal intervals in the toe-heel and crown-sole directions around the center point Pc of the face 1402. A dedicated swing robot was used to swing the golf club at the 45 impact points Pi, and the initial velocity of the golf ball was measured using a measuring device. The head speed was 40 m / s. The initial velocity data from the 45 impact points was interpolated, and the area of ​​the high initial velocity area on the face 1402 that achieved 98% or more of the maximum initial velocity of the golf ball was indexed. Note that data from impact points above the center point Pc (closer to the crown 16) and below (closer to the sole 18) were weighted more heavily to match the actual impact point location of the golfer. The data for the high initial velocity area was expressed as an index, with the measurement result of the golf club head in Experimental Example 1 set to 100. A higher index indicates a better evaluation.

[0050] (2) Launch Angle The launch angle obtained in the actual hitting test at the above impact point position was measured. The index of Experimental Example 1 was set to 100, and the larger the index, the greater the launch angle and the better the evaluation.

[0051] (3) Spin Rate Based on the spin rate (backspin rate) obtained in the actual hitting test at the impact point Pi, the index for Experimental Example 1 was set to 100, with a larger index indicating a lower spin rate and a better evaluation.

[0052] (4) Impact Feel The impact feel is dominated by the impact sound produced when the golf club head strikes the ball. Generally, an impact sound with a moderately short reverberation and low pitch is considered to have a soft, pleasant impact feel, leading to a high evaluation by the golfer. The impact feel is evaluated as follows: Using a dedicated swing robot, a golf club is swung at a head speed of 40 m / s with the center point Pc as the impact point. The impact sound of the golf ball is measured using a sound level meter, and vibration waveform data of the impact sound is sampled and recorded at a predetermined sampling period. Next, a reverberation parameter T is calculated. The reverberation parameter T is a parameter that represents the degree of attenuation of the impact sound. To calculate the reverberation parameter T, the first sample data (starting point data) on the time axis of the recorded vibration waveform data is assigned a reference number. Starting from this number, a block group α is created in which the sound pressure vibration waveform is sequentially divided into blocks every predetermined number of samples, for example, 100 samples. The sum of squares of the vibration waveform levels is then calculated for each block Ak in the block group α, and the logarithm of this sum of squares (hereinafter referred to as the block value) is calculated for each block. The maximum sound pressure block with the largest block value is then extracted as the starting block from each block in the block group α. A value lower than the block value of this maximum sound pressure block by a predetermined value (30 dB in this embodiment) is then set as the end block value. Among the blocks following the starting block, the end block whose block value is the first to fall below the end block value is extracted. The time width between the earliest sample data on the time axis for each of these starting and end blocks is then set as the reverberation parameter T. Therefore, the reverberation parameter T corresponds to the reverberation time of the impact sound. The shorter the reverberation parameter T, the shorter the reverberation, the softer the impact feel, and the higher the impact feel evaluation. In this case, the impact feel data is expressed as an index, where 1 / T, the inverse of the reverberation parameter T of the golf club head in Experimental Example 1, which corresponds to the comparative example, is set to 100. The higher the index, the better the impact feel evaluation. The reverberation parameter T can be calculated using the method described in Japanese Patent No. 4840106, for example. However, there are no limitations on the method for evaluating the reverberation time of the hitting sound, and it is possible to obtain the reverberation time of the hitting sound and evaluate the hitting feel using various conventionally known methods.In addition to evaluating the feel of the impact by calculating the reverberation parameters and reverberation time, the feel of the impact may also be evaluated by having a golfer actually swing a golf club to hit a ball and listening to the impact sound.

[0053] (5) Durability Golf balls were repeatedly hit with an air cannon against the face 1402 of a golf club head fixed to a shaft, and the number of hits required until deformation or damage to the face portion 14 occurred was measured and indexed. The ball speed was set to 50 m / s. The impact point was set to the center point Pc of the face 1402. In this case, the measurement result of the golf club head of Experimental Example 1, which corresponds to the comparative example, was expressed as an index of 100. The higher the index, the better the evaluation.

[0054] (6) Total Score The total score was calculated by adding up the five indices of the high initial velocity area, launch angle, backspin, feel, and durability. The total score for Experimental Example 1, which corresponds to the comparative example, was 500, and the higher the total score, the better the evaluation.

[0055] The experimental conditions will be explained. Experimental Example 1 is a comparative example and corresponds to Patent Document 1 (Japanese Patent No. 4340177) cited in the prior art. It is a golf club head in which the face portion is constructed of a first metal plate and a second metal plate that supports the first metal plate via a plurality of ribs. Experimental Example 1 does not satisfy the provisions of claim 1 and is outside the scope of the present invention. The specifications of each part of Experimental Example 1 are as follows: Head body material: titanium alloy Ti-8Al-1Mo-1V Face material: titanium alloy Ti-6Al-4V Loft angle 10.5° Lie angle 59° Head mass 200g Head volume 460cc

[0056] The golf club head used in Experimental Example 2-25 corresponds to the present invention and is a hollow driver. Except for the parameters specified in each experimental example, the following specifications were common to all the golf club heads: loft angle: 10.5°, lie angle: 59°, head mass: 200 g, head volume: 460 cc. The golf club head used in Experimental Example 2-25 was constructed with the structure of the fourth embodiment ( FIG. 5A ). The materials constituting the first layer 36, second layer 38, and third layer 40 in Experimental Example 2-25 are shown in FIGS. 12-15 . Typical tensile strengths of materials include titanium alloy (6-4Ti) at approximately 1047 MPa, CFRP (long fiber) at approximately 1250-2500 MPa, polyurethane at approximately 200-450 MPa, polycarbonate at approximately 65 MPa, and vinyl chloride at approximately 50 MPa.

[0057] (Condition 1: Figure 12 / Experimental Examples 2-8) In Figures 12 to 15 below, the symbol ◯ in the column for tensile strength S3 ≧ S1 > S2 indicates that the tensile strength condition is met, and the symbol × indicates that the tensile strength condition is not met. As shown in Figure 12, Experimental Example 1 is a comparative example and is outside the scope of the present invention. Experimental Examples 2-8 all satisfy the tensile strength S3 ≧ S1 > S2 specified in claim 1. Experimental Examples 2-8 all satisfy the provisions of claims 1, 2, 3, 4, and 5. Furthermore, Experimental Example 8 satisfies the provisions of claim 6 (uneven thickness structure) in addition to claims 1, 2, 3, 4, and 5. The uneven thickness structure of Experimental Example 8 is the same as that of the third embodiment (Figure 4(B)). Therefore, compared to Experimental Example 1, which is outside the scope of the present invention, Experimental Examples 2-8, which are within the scope of the present invention, are superior in high initial velocity area, launch angle, backspin, durability, hit feel, and total score.

[0058] (Condition 2: Figure 13 / Experimental Examples 9-17) Of Experimental Examples 9-17, Experimental Examples 9, 10, 13, 16, and 17 do not satisfy the requirements of claim 1 and at least claim 2 (hardness of the first layer 36, second layer 38, and third layer 40), and are outside the scope of the present invention. The remaining Experimental Examples 11, 12, 14, and 15 satisfy the requirements of claim 1 and at least claim 2. Note that in Figure 13, the hardness M70 of the second layer 38 of Experimental Example 10 indicates Rockwell hardness. Therefore, compared to Experimental Examples 9, 10, 13, 16, and 17, which do not satisfy the requirements of claim 2, Experimental Examples 11, 12, 14, and 15, which satisfy the requirements of claim 2, are superior in high initial velocity area, launch angle, backspin, durability, feel, and total score.

[0059] (Condition 3: Figure 14 / Experimental Examples 18-21) Of Experimental Examples 18-21, Experimental Examples 18 and 19 satisfy the provisions of claim 1, but do not satisfy the provision regarding the thickness of the second layer 38 among the provisions of claim 4 (thicknesses of the first layer 36, second layer 38, and third layer 40), and are therefore outside the scope of the present invention. The remaining Experimental Examples 20 and 21 satisfy the provisions of claim 1 and at least the provisions of claim 4. Therefore, compared to Experimental Examples 18 and 19, which do not satisfy the provisions of claim 4, Experimental Examples 20 and 21, which satisfy the provisions of claim 4, are superior in high initial velocity area, launch angle, backspin, durability, feel, and total score.

[0060] (Condition 4: FIG. 15 / Experimental Examples 22-24) Experimental Examples 22-24 differ in head volume, and all satisfy the provisions of claims 1 to 4. Therefore, compared to Experimental Example 1, which is outside the scope of the present invention, Experimental Examples 22-24, which are within the scope of the present invention, are superior in high initial velocity area, launch angle, backspin, durability, hit feel, and total score.

[0061] In this embodiment, the golf club head is a hollow wood-type golf club head (driver), but the present invention is of course also applicable to hollow utilities and fairway woods.

[0062] DESCRIPTION OF SYMBOLS 100 Golf club 10A, 10B, 10C, 10D Golf club head 12A, 12B, 12C, 12D Head body 14 Face portion 1402 Face surface 16 Crown portion 18 Sole portion 20 Side portion 22 Hollow portion 24 Toe 26 Heel 28 Hosel 30 First face member 3002 Protrusion 32 Second face member 34 Face portion plate portion 3402 Protrusion 36 First layer 38 Second layer 40 Third layer 4002 Thin portion 4004 Recess 42 Elastic adhesive 44A, 44B Epoxy adhesive 46 Double-sided tape 48 Ring-shaped synthetic resin 49 Paint 50A, 50B, 50C Urethane sheet 52 First face member 5202 Protrusion 54 Second face member 56 Third face member 5602 Protrusion 58 Opening 60 Face outer periphery 62 Outer periphery plate portion 64 Protruding plate portion 66 Inner periphery plate portion 68 Bead accommodating space B Bead 70 Gap 71 Paint 72 First face member 7202 First face body 7204 First flange 74 Second face member 7402 Second face body 7404 Second flange 76 Third face member 7602 Third face body 7604 Third flange 78 Opening 80 Bead accommodating space 82 Synthetic resin 83 Paint

Claims

1. A golf club head having a hollow structure in which at least a portion of the face portion is composed of a first layer constituting the face surface, a second layer located on the opposite side of the first layer to the face surface, and a third layer located on the opposite side of the second layer to the first layer, wherein when the tensile strengths of the first layer, second layer and third layer are S1, S2 and S3 respectively, S3 ≧ S1 > S2.

2. The golf club head according to claim 1, characterized in that the first layer has a hardness of at least D75 on a durometer scale and at most HV520 on a Vickers scale, the second layer has a hardness of at least A10 on a durometer scale and at most D60 on a durometer scale, and the third layer has a hardness of at least D85 on a Vickers scale and at most HV520 on a durometer scale.

3. The golf club head according to claim 1, characterized in that the first layer has a tensile modulus of elasticity of 8 GPa or more and 240 GPa or less, the second layer has a tensile modulus of elasticity of 0.5 MPa or more and 3000 MPa or less, and the third layer has a tensile modulus of elasticity of 10 GPa or more and 240 GPa or less.

4. The golf club head according to claim 1, characterized in that the thickness of the first layer is 0.1 mm or more and 1.5 mm or less, the thickness of the second layer is 0.1 mm or more and 1.0 mm or less, and the thickness of the third layer is 2.0 mm or more and 5.0 mm or less.

5. A golf club head according to claim 1, characterized in that the first layer is made of any one of a metal material, a synthetic resin material, or a fiber-reinforced resin material, the second layer is made of any one of a double-sided tape, a synthetic resin material, or an elastic material, and the third layer is made of any one of a metal material, a synthetic resin material, or a fiber-reinforced resin material.

6. A golf club head according to claim 1, characterized in that the third layer has a thin portion that is thinner than other portions, the thin portion being composed of a recess formed in the first layer in an open manner on the front surface of the third layer facing the first layer, and the second layer is arranged by filling the recess.

7. The golf club head according to claim 6, wherein said front surface of said third layer excluding said recessed portion is superimposed on said first layer.

8. The golf club head comprises a hollow head body including a face outer periphery in which an opening is provided except for the outer periphery of the face part, and a crown part, a sole part and a side part connected to the face outer periphery, the plate-shaped third face member constituting the third layer is provided on the inner side of the head body inside the face outer periphery, the plate-shaped second face member constituting the second layer is attached to the third face member by overlapping it inside the face outer periphery, the plate-shaped first face member constituting the first layer is attached to the second face member by overlapping it inside the face outer periphery, the third face member is attached by welding with its outer periphery abutted against the inner periphery of the frame-shaped inner peripheral plate part of the face outer periphery, a bead generated during the welding is accommodated in a bead accommodation space provided across the outer periphery of the third face member and the inner periphery of the attachment plate part on the side away from the inside of the head body, and the bead accommodation space is covered by the second face member and the first face member.

2. The golf club head according to claim 1.

9. The golf club head comprises a hollow head body having an opening formed by removing the face portion, a portion of the crown portion near the face portion, a portion of the sole portion near the face portion, and a portion of the side portion near the face portion; the third face member constituting the third layer comprises a third face body corresponding to the face portion, and a third flange protruding from the outer periphery of the third face body toward the head body; the second face member constituting the second layer comprises a second face body attached to be superimposed on the third face body, and a second flange protruding from the outer periphery of the second face body toward the head body and attached to be superimposed on the third flange, the portion of the crown portion near the opening, the portion of the sole portion near the opening, and the portion of the side portion near the face portion; the first face member constituting the first layer comprises a first face body attached to be superimposed on the second face body, and a first flange protruding from the outer periphery of the first face body toward the head body and attached to be superimposed on the second flange; 2. The golf club head according to claim 1, wherein a tip end face of the third flange is butted against the tip end face of the crown portion, the tip end face of the sole portion, and the tip end face of the side portion which form the opening, and is attached by welding, a bead created during the welding is contained in a bead accommodating space provided across the outer periphery of the third flange, the outer periphery of the crown portion, the outer periphery of the sole portion, and the outer periphery of the side portion on the side away from the inside of the head body, and the bead accommodating space is covered by the second face member and the first face member.

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